Fifty nine of the 280 percutaneous mitral valvuloplasties (21%) performed between March 1987 and December 1991 at the Montreal Heart Institute were carried out for symptomatic mitral restenosis 15 +/- 6 years after surgical commissurotomy. The patients were selected according to echocardiographic criteria. The mitral valve disease was comparable to that of patients without previous surgical commissurotomy. Patients with good hemodynamic result had undergone surgical commissurotomy more recently and had less severe valvular damage than patients with an incomplete (n = 10) or poor result (n = 7). One patient died of a cerebral embolism during the procedure, two patients underwent emergency surgery for a mitral valve rupture and 4 patients had an atrial septal defect with Qp/Qs ratio greater than 1.5 by oximetry. The numbers of successes and complications were comparable to those observed in patients without previous surgical commissurotomy. The patients who had undergone previous surgical commissurotomy were followed up for 1 year. At 12 months, 4 remained in Class II of the NYHA classification, 44 (74%) were improved by at least 1 functional class and 10 (17%) had required a mitral valve replacement. Percutaneous mitral valvuloplasty is therefore a useful procedure in patients with moderate degrees of valvular disease who develop restenosis after surgical commissurotomy. A functional improvement can be expected in 3/4 of patients Complications related to the procedure are rare and acceptable compared with the risks of a second thoracotomy. Failure of percutaneous mitral valvuloplasty is generally due to the degree of valvular disease which contraindicated surgical commissurotomy and required mitral valve replacement.